1. Field of the Invention
This disclosure relates to the field of air purification and converting air which is unsafe for human use into air which humans can safely breathe. In particular, this disclosure relates to the use of supercritical water oxidation to purify air.
2. Description of the Related Art
In recent years the need to segregate individuals from dangerous substances in the air has become one of increasing interest. All human beings must breathe and the introduction of airborne agents into the air they inhale creates a dangerous situation whereby individuals can be killed or injured and can strain medical response capability in an area. While all environmental air contains some impurities which can harm those breathing it, such as cold viruses and allergen molecules, modern warfare, terrorism, technology changes, and increasing globalization have led to an increased likelihood of larger scale contamination of air where sources of clean air can become quickly necessary to prevent catastrophic outcomes.
The danger of a chemical, biological, or nuclear weapon being unleashed on military forces, or on civilian centers, is a nightmare scenario for many government organizations. Such an attack can stymie military effectiveness or bring day to day economic activity to a grinding halt. Even without the purposeful use of nuclear, biological, or chemical weapons, the possibility of accidents involving these agents in populated areas is also a danger and governments must be able to respond to protect the citizenry. Still further, increases in globalization have led to increased danger of communicable disease. The recent Severe Acute Respiratory Syndrome (SARS) outbreak and fear of other dangerous natural contagions transmitted in the air has dramatically highlighted the need for clean air. In public forums such as stadiums, malls, convention centers, or airplanes where a large population is breathing the same air, it is desired to have air handling systems able to remove contaminants to prevent widespread exposure to a contagion. Further, in the event of a catastrophic incident, governments and emergency response agencies need to be able to quickly provide safe working conditions for health workers and other emergency responders to contain and destroy contaminants, whether natural or man-made, whenever and wherever may be necessary.
From the above, the need to provide safe air supplies may come upon a population suddenly, may be preferable but not necessarily required in anticipation of a potential release, or may be constant such as in hospitals or “clean rooms,” where the need for cleaned air is always necessary as environmental air is simply too dirty for the specialized use to which the air is put. The need for decontamination may be known or predicted or an increased risk may be known to be likely in some situations. In other situations it may come without warning.
An airborne contaminant's danger level will generally depend on concentration. The concentration of a contaminant in the air being breathed will generally need to be above a particular threshold or else exposure is unlikely to cause concern. Most contaminants, if sufficiently dispersed, are not particularly dangerous. Therefore, protection against contamination usually requires the ability to either provide air which is known to be safe and has been stored for use during the contamination period, or to filter air which is contaminated to remove the contamination and provide safe air. The use of stored air is generally less effective as the storage requires specialized tanks and processes, and generally the amount of air which can be stored is relatively small. Instead, filtration is generally used, particularly if one is attempting to provide safe air to a group of individuals.
Filtration for harmful contaminants generally works by pulling some or all of the contaminant from the air into a solid filter. The resulting air is then provided to the users and generally only includes a reduced concentration of the contaminant such that the levels are sufficiently low that the contaminant is no longer harmful or, at the worst, no longer debilitating.
To prevent introduction of contaminants later, the clean air is generally pumped into an isolation environment which prevents introduction of unfiltered air and in which the individuals needing air are located. Smaller protective suits can provide an isolation environment for a single person while larger isolation structures can house multiple individuals. These isolation structures are, therefore, often the preferred method of providing safe air. Isolation structures can have economies of scale for filtration where larger more powerful air intake devices can be used to supply air to the structure. Further, a structure can allow individuals therein to perform tasks as they normally would instead of being forced to work in cumbersome individual protective suits.
Isolation structures may be permanent or may be temporary and may be used in any environment where safe air is needed. These environments may not be suitable for human occupancy because air is contaminated, or because air simply does not exist. In emergency responses or military field activities on the Earth, a temporary structure is generally preferred as it can be quickly setup anywhere when needed, and more easily stored when not needed. Often the temporary structure is inflatable whereby the structure can be setup in the zone of contamination and can then be filled with clean air using a portable filtration system to filter outside environmental air. The internal air pressure then provides the shape to the structure. Once inflated, the structure will be able to provide a safe haven for multiple people and a staging point for the use of contamination suits to venture further into a contaminated area. Further, the structure can often be provided with more efficient heating, cooling, or other environmental control units (ECUs) than individual protective suits can include.
FIGS. 1 and 2 provide for a first embodiment of an isolation shelter, in particular a collective protection shelter of the type commonly used by the United States military. This structure is intended to be vehicle portable (as shown in FIG. 2) and is usually transported on a High Mobility Multipurpose Wheeled Vehicle (HMMWV or Humvee) (70). Once deployed, as it is in FIG. 1, the shelter (75) will have been inflated and will comprise a self supporting isolation shelter. In the depicted embodiment, the shelter (75) comprises two structural “buildings” connected side-by-side. There is also an external airlock allowing access inside the shelter (75). The Humvee (70) is still attached to the shelter (75) and generally serves as a command and control center for the shelter (75) as well as a power source via its engine to run components in the shelter (75). In an embodiment, the collective protection shelter will also generally have an environmental control unit (ECU) (not shown) and may include an external generator.
Traditionally, on both portable filtration units and in permanent structures, filtration was performed by use of deep bed activated carbon filters or similar filters which block particles larger than a particular size and/or that react with particles of a particular type.
While this type of system is well understood, filters of this type all suffer from similar drawbacks. In the first instance, changing the filter generally requires a potentially hazardous operation. As contaminants are captured by the filter to clean the air, the filter therefore will contain a high concentration of contaminants which will often make the filter quite toxic. These contaminants are generally still dangerous and biologically active within the filter material. Therefore, individuals handling the filter need to be careful that they are not accidentally exposed to the contaminants or that they do not inadvertently introduce the concentrated contaminants into an unfiltered air stream. In many respects, the filter cleans the air while creating a dangerous solid waste (namely the filter itself) which has to be safely disposed of to avoid later contamination. The contaminant is not eliminated by the filtration, it is simply concentrated and captured in a more easily disposable form.
Filters of the traditional type also have the problem of failing after a certain amount of time. As a filter is used, the ability of the filter to successfully filter out additional contaminants is often compromised and a dirty filter can reintroduce contaminants to the filtered air. Further, as filters become full of contaminants the air flow is often slowed so that motors drawing air into the structure must work harder or an insufficient amount of air is provided. As humans generate carbon dioxide while breathing, which is toxic to them, with insufficient clean air flow into the system, air can rapidly become dangerous even if outside contamination is successfully removed.
Filters are also part of the significant logistic trail in both military and civilian protection and can also be a significant expense. To date, there is no production system that incorporates a method to measure the absorbent capacity level remaining in filtration material. In the absence of this, protocol dictates that a filter be changed after a predetermined number of hours in service, irrespective of whether it has filtered contaminated air or not. This means that the filter is changed more frequently than may be needed when it is in use to prevent any unintended failure. Each change of filter requires personnel to leave the isolation environment and to change the filter. As well as being a tedious and dangerous task, it offers the possibility that the new filter might not seat correctly, leaving the system potentially at risk and introducing the danger that personnel may be exposed to the contaminated air while outside the shelter.
One proposal to attempt to deal with the need to change filters is regenerative filtration whereby the filter can be remotely cleaned. There have been numerous different types of these proposed such as pressure swing, temperature swing, electronic swing and hybrid systems thereof. Regenerative filtration systems, while effective, are bulky and consume more power and, hence, are only useable in certain applications. Further, regenerative filters provide no energy recovery but actually use additional energy to operate as they must have power to clean. Further, the regenerative filter cannot provide aid to the other environmental control aspects of the ECU. The regenerative filter does not provide for heating or cooling of the air which must be provided by the ECU. This makes the regenerative filter an expensive alternative. Finally, a regenerative filter is still generally a standard filter, and while it can self-clean is generally subject to the limitations on air flow and contaminant capture as a more traditional filter.